New devices for the broad screen detection of contaminants or pollutants in a solution or in a gas phase are widely desired for use in evaluation of, e.g., water supplies, hazardous waste sites, and work place environments. Many present forms of such, analyses involve the use of expensive instrumentation. For example, analysis of water supplies for total chlorine content, chlorocarbons, or pesticide residues requires the use of high performance liquid chromatography, mass spectroscopy or UV-VIS spectroscopy. At hazardous waste sites, ground water and surface water are analyzed in a similar fashion. Detection of volatile organic hydrocarbons (VOCS) in soils, on the other hand, involves the head space analysis of the vapor above the soil samples through the use of gas chromatography. Detection of pesticide residues involves mass spectroscopic analysis of chromatographically separated samples.
It is known that metal ions can be detected through a color change brought about by the reaction of the ions with a ligand or chelating agent. Metals can inhibit the activity of enzymes, an aspect that can be used to quantify their concentration. They can also stimulate the activity of enzymes through the release of substrates for the enzyme; this heightened activity can also be: quantified. Such methods are known to be applicable to molecules and ions other than metals.
Immunoassay methods are known to be sensitive in their response to target analytes. Biologically active organisms such as Helicobacter pylori and Streptococcus species can be detected. The antibody-antigen interaction is utilized to produce a detectable event upon exposure of the device to the target analyte. Fluorescent species can be released that can be detected instrumentally; electrochemical means can be used to amplify the signal. Interference patterns can be induced by such reactions through a change in film thickness, which can be quantified.
Many of these analytical methods have been assembled in analytical devices with a multilayer construction that separates an analyte detection from the readout function. There are several strategies in the art of multilayer analytical elements which have been devised for detection of specific molecules, ions, contaminants, or pollutants.
It is well known that metal ions in solution such as ferrous or ferric ions, calcium, lead or zinc can be detected through such a multilayer element. The target analyte reacts with a reagent within one of the layers of the device to produce a colored change that can be quantified calorimetrically. The concentration of the colored species can be assessed visually through a comparison with standards or measured with an instrument in either a transmissive or reflective mode. In the reflective mode, the detection layer resides upon a transparent polymer base but in front of a reflective pigment layer.
The detection of metal ions can be accomplished through a number of variations on this procedure. Ferrous ions can be chelated by reagents within a multilayer element that provides a buffered environment for its migration to a detection layer. The chelating agent may be resident in this detection layer. Similar arrangements are known for the detection of Ca++ in aqueous solutions. Interferences may be removed by the presence of additional reagents such as the addition of calcium chelating reagents to a multilayer analytical element designated for detection of magnesium.
Multilayer analytical elements have been devised for the assay of complex fluids, such as blood. Such elements can be composed to detect glucose, alcohol, cholesterol, or proteins. In the analysis of such complex fluids, separation layers impregnated with separation agents are used to isolate the target analyte from the other components of the blood. Such analyses of biological fluids often rely upon enzymes to produce the color change for detection of the target analyte. The analyte can interfere with a color-producing reaction by the enzyme, or it can induce the enzyme to produce a colored species.
Immunoassay methods make use of antibody/antigen binding to effect specific sensitivity in multilayer analytical elements. Enzymes specific to an analyte are synthesized and coated within such a device to bind the target molecule and induce a measurable readout signal through the release of a molecule which can migrate to a registration layer. Usually this is a fluorescent assay that requires a photodetector for interpretation.
In the present invention, a novel means of broad screen detection is described for the presence of target analytes in the vapor phase, in solution, or eluted from a solid. In the invention, the novel application of competitive dye desorption from a solid adsorbent is employed as a method of quantifying the presence of the molecule or target analyte. In the function of an analytical element for implementing the competitive dye desorption method of the invention, dye or dye-precursor molecules adsorbed on the surface of an adsorbent are caused to desorb through the adsorption of the target analyte on the adsorbent. The desorbed dye or precursor is made detectable through sequestering of a radiation detectable species in the device of the invention. Such detection may occur, e.g., through absorption or emission of radiation in regions of the spectrum extending from the ultra-violet through the visible and into the infra-red regions.
In one aspect of the invention, these processes occur within a multi-layer analytical element, in which the functions of the device may be executed by different layers. Such an integral, multi-layer element will include an analyte acquisition layer, which contains the substrate for dye desorption from which dye is desorbed in response to the presence of the analyte within the layer, and an underlayer in which the desorbed dye is sequestered in a detectable manner.